This invention relates to the field of starter motors, and more particularly to starter motors for use with marine engines.
In internal combustion engines, the electro-mechanical functions of starting and power generation have traditionally been accomplished by separate discrete units. In particular, a cranking motor has been used for starting the engine, and a separate alternator has been used for generating electrical power from the work performed by the engine. With the advent of high power density per dollar inverters and low cost micro-controllers, integration of the starter motor and the alternator into a single unit has been practically achieved. Integrated starter motors and alternators vary in power output capability from low power starter-alternators to high power hybrid propulsion systems.
Marine engines are uniquely qualified for utilization of an electro-mechanical device that integrates the starter motor and the alternator. The marine application provides a more suitable environment for an integrated starter-alternator because of the lower cranking requirements, lower generating requirements, and an abundant source of water for cooling. Because of these factors, the control and power electronics used in marine integrated starter-alternators can be even more affordable than those used on automobile applications.
In addition to the electro-mechanical functions of starting and power generation, owners of marine engines often desire a separate electric motor application that is not required in any other industry. In particular, marine engine owners often desire a separate electric motor for xe2x80x9ctrolling,xe2x80x9d i.e., quietly propelling a boat through the water at a slow speed. Electric trolling motors are generally separate from the engine and are equipped with their own propellers. The most common use of the electric troller motor is for fishing. It may also be advantageous for boat owners to troll when leaving or entering the dock. Trolling is advantageous during this time to reduce emissions and avoid engine stall when traveling at low speeds around the dock.
If a fisherman desires to troll during his fishing trip, he must remember to bring along the trolling motor. Although the trolling motor may be stored on the boat, many boats do not have a safe place to store items such as trolling motors, and leaving the trolling motor on board when the boat is docked would invite theft of the trolling motor. Thus, most fisherman must carry their trolling motors to their boats before embarking on a fishing trip. Should a fisherman forget to bring his or her trolling motor when embarking on a fishing trip, he will not be able to troll during the trip.
In addition to remembering the trolling motor, the fisherman must also mount the trolling motor on the boat before it is used. Although mounting is usually a simple task, such as simply hooking the motor to the boat hull, it is nevertheless an inconvenience. Next, after the motor is mounted, it must be connected to the battery which provides electric power to the motor. After remembering to bring the motor and after properly mounting the motor and connecting it to the battery, the fisherman is finally ready to use the motor for trolling.
As discussed above, marine power applications generally require at least two and sometimes three separate electro-mechanical devices. Specifically, these devices are (1) cranking motors for starting, (2) alternators for power generation, and (3) trolling motors for slow and silent propulsion of the boat through the water. These discrete units take up a great deal of space in marine applications. Furthermore, the combined cost of each of these units is significant. Therefore, it would be advantageous if a single electro-mechanical device could be used to provide all three functions of starting, power generation, and trolling. Combining these units could save on a great deal of engine size and cost. Furthermore, integration of the starter-alternator of a marine engine with the trolling motor would provide the owner of the marine engine the opportunity to troll without having to remember a separate trolling motor when embarking on a fishing trip and without having to mount a separate motor to the boat.
For the foregoing reasons, there is a need for a single electro-mechanical device for use with an internal combustion marine engine that is operable to serve as a cranking motor for starting the engine, a generator for generating electrical power from the engine, and a trolling motor for providing quiet propulsion power when the engine is not in use.
The present invention is directed to a device that satisfies this need for combining the functions of starting, power generation, and electric propulsion in a single electro-mechanical device for a marine engine. The electro-mechanical device comprises three phase stator windings positioned across an air gap from a rotor winding. The rotor winding is fixed to the interior cup surface of a flywheel having a drive shaft extending through the center of the flywheel. The drive shaft is releasably connected at one end to a crankshaft of an internal combustion engine by an electric clutch. At another end, the drive shaft is connected to a transmission which drives a propeller.
The electro-mechanical device further comprises an active rectifier bridge having a plurality of transistor switches connected to the three phase stator windings. A controller is in communication with the active rectifier bridge and controls the active rectifier bridge such that the electro-mechanical device operates in one of several modes. In a first mode, the controller receives a starting mode command and operates the active rectifier bridge to cause the electro-mechanical device to act as a starting motor to crank the internal combustion engine. In a second mode, the controller senses that the engine has fired and automatically operates the active rectifier bridge to cause the electro-mechanical device to operate as a generator during operation of the internal combustion engine. In a third mode, the electric clutch disconnects the rotor drive shaft from the internal combustion engine crankshaft. At the same time, the controller receives an electric propulsion mode command and operates the active rectifier bridge to cause the electro-mechanical device to operate as an electric propulsion motor and provide propulsion power for the boat apart from the internal combustion engine.
These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.